Nexus dome offering changes

FYI

Nexus has discontinued the glass 160 dome, according to a distributor. New orders are not being accepted for it.

In the Dec/Jan time frame, the 170 dome will be switched to glass with a substantial (> 50%) price increase.

Hi Dave,

Do you know if the 170 glass is hemispherical or a sectioned dome? I have a very old 170 acryllic and despite being a larger diametre than the 160 glass the corners were softer because it was hemispherical, more curvature toward the edges.

Thanks

Mary

Mary - what setups are you using with 170 port? For 12-24 lens I use 40mm ext ring & +4 diopter with very good results. For 10-17 (which I just got) a 20mm ring is looking good. These are the best setups I've found so far for corner sharpness.

Mary - what setups are you using with 170 port? For 12-24 lens I use 40mm ext ring & +4 diopter with very good results. For 10-17 (which I just got) a 20mm ring is looking good. These are the best setups I've found so far for corner sharpness.

I have been using the 170mm dome 40mm extension +4 for the 12-24 lens and 230mm for the 10-17 I have been happy with the corners, especially the 230mm dome

However, I have just purchased from Yuzo the 160mm glass with 15mm extension. I had a 20mm extension already but Yuzo suggested I would get vignetting from the shade. I did tests in the backyard with the 160mm dome 20mm extension and got vignetting in 2 corners only. This may not happen with the new 170mm dome.

Yet to try the 160mm glass and 15mm extension for the 10-17 underwater. So when I said the 160mm had better corner sharpness than the 170mm that test was done with a borrowed 160mm some time ago and I didn't have any extension. So adding the extension will only be better.

I was just curious as to the design of the new 170mm.

Mary

Just for reference - when I was trying to set up my 17-55 lens I measured & tested an old FP160 glass dome & the FP170 acrylic dome that I was using with a Nexus D70. The 160 had a radius of curvature of 87.5mm (175mm dia), with center located 37.5mm aft of base plate. Hence it's a spherical section. The 170 had a radius of 85mm (170mm dia), with center located 20mm aft of base plate. Still not a full hemisphere, but a larger spherical section than the 160. So 160 & 170 represent base diameters of the actual sections, not of the corresponding spheres. A true hemisphere would have the center of curvature located at the base plate.

P.S. Regarding the 17-55 zoom, neither port was satisfactory - both had soft edges & corners. The 160 was actually worse. I ended up using the Custom 12-24 port, which happens not to work with the 12-24 lens do to vignetting at 12-14mm zoom range. Using +3 or +4 diopter with 17-55, depending on focus range I need.

Thanks Jim for that detailed explanation,

I had to read it a couple of times to get my head around it. I stand corrected when I said the 170mm dome was hemispherical.

So, before introducing any extensions, like in my test explained above, and because the 170 has a larger spherical section, its image corners are softer (compared to the 160) due to the light that has hit the corners of the sensor has come through the dome at a smaller angle. Have I got that right?

When I look at both domes the 160 is "shallower" in design and that's why I thought it gave me sharper corners.

Is your 12-24 port shallower again?

Thanks

Mary

The Custom 12-24 port is even a smaller spherical section than the 160, but with a larger radius. I measured it's radius of curvature to be 95mm (190mm dia) with center 20mm aft of the elongated base (like a built in ext ring). Extension rings are used to position the dome center of curvature at the nodal point of the lens. My rather basic testing has shown that this placement mostly effects corner/edge sharpness. The center of the frame always seems to look pretty good.

I ended up using the Custom 12-24 port, which happens not to work with the 12-24 lens do to vignetting at 12-14mm zoom range. Using +3 or +4 diopter with 17-55, depending on focus range I need.

Absolutely, I use exactly the same set-up!

Still experimenting with the Tokina 10-17mm, tho' my acrylic Nexus 170mm has done well.

Tim

So far the only difference I've heard or read about the 10-17 with FP170 port vs Custom 10-17 port is size & about $900 (assuiming you already have the 170). Nothing definitive in photo quality. Would like to hear more about this comparison from others that have shot with each setup.